This invention relates to improvements in the process for manufacturing paper envelopes and the like. More particularly, it relates to the use of a microencapsulated glue in the manufacturing process.
In the manufacture of envelopes from an envelope sheet, two kinds of glue are normally used. For the bottom and side portions which are "permanently" sealed together, a back gum containing from about 60 to about 70 percent of solids is used. On the envelope flap, a remoistenable seal gum is applied. In the process of manufacture normally used, the first step is to apply the remoistenable seal gum to the portion of the envelope sheet, which will later become the lid of the envelope. This is done, for example, by collating a number of envelope sheets so that approximately 9/16 inches of the lid portion of each envelope sheet is exposed. The glue, in liquid suspension, can then be conveniently rolled on. The coated envelope sheet is then dried. Each envelope sheet is then scored in the places where folds are desired and back gum is applied to the portion of the envelope sheet where the bottom flap and the side flaps will be sealed. The back gum is also applied in liquid suspension or solution. The bottom and sides are then immediately folded up to finish the envelope.
One of the disadvantages of this process is that, once the back gum is applied, the bottom and side flaps must be immediately folded up and sealed. For reasons of storage and handling, it would be desirable to be able to apply the back gum without immediately folding the bottom and side flaps. At the present time, it is not possible to collate envelope sheets on which both the seal gum and the back gum has been applied.
It would also be advantageous to apply the seal gum in the form of microcapsules to the seal flap as this would permit the end user to seal the envelope without moisture. This feature would be of particular advantage to large mailers using inserting machines.
It is therefore a principal object of this invention to provide a more flexible process for the manufacture of envelopes in which both the seal gum and the back gum can be applied to the envelope sheet and the sheets then collated without first having to perform the step of sealing the bottom and sides.